Posts Tagged ‘criterias’

Secure Apache webserver against basic Denial of Service attacks with mod_evasive on Debian Linux

Wednesday, September 7th, 2011

Secure Apache against basic Denial of Service attacks with mod evasive, how webserver DDoS works

One good module that helps in mitigating, very basic Denial of Service attacks against Apache 1.3.x 2.0.x and 2.2.x webserver is mod_evasive

I’ve noticed however many Apache administrators out there does forget to install it on new Apache installations or even some of them haven’t heard about of it.
Therefore I wrote this small article to create some more awareness of the existence of the anti DoS module and hopefully thorugh it help some of my readers to strengthen their server security.

Here is a description on what exactly mod-evasive module does:

debian:~# apt-cache show libapache2-mod-evasive | grep -i description -A 7

Description: evasive module to minimize HTTP DoS or brute force attacks
mod_evasive is an evasive maneuvers module for Apache to provide some
protection in the event of an HTTP DoS or DDoS attack or brute force attack.
It is also designed to be a detection tool, and can be easily configured to
talk to ipchains, firewalls, routers, and etcetera.
This module only works on Apache 2.x servers

How does mod-evasive anti DoS module works?

Detection is performed by creating an internal dynamic hash table of IP Addresses and URIs, and denying any single IP address which matches the criterias:

  • Requesting the same page more than number of times per second
  • Making more than N (number) of concurrent requests on the same child per second
  • Making requests to Apache during the IP is temporarily blacklisted (in a blocking list – IP blacklist is removed after a time period))

These anti DDoS and DoS attack protection decreases the possibility that Apache gets DoSed by ana amateur DoS attack, however it still opens doors for attacks who has a large bot-nets of zoombie hosts (let’s say 10000) which will simultaneously request a page from the Apache server. The result in a scenario with a infected botnet running a DoS tool in most of the cases will be a quick exhaustion of system resources available (bandwidth, server memory and processor consumption).
Thus mod-evasive just grants a DoS and DDoS security only on a basic, level where someone tries to DoS a webserver with only possessing access to few hosts.
mod-evasive however in many cases mesaure to protect against DoS and does a great job if combined with Apache mod-security module discussed in one of my previous blog posts – Tightening PHP Security on Debian with Apache 2.2 with ModSecurity2
1. Install mod-evasive

Installing mod-evasive on Debian Lenny, Squeeze and even Wheezy is done in identical way straight using apt-get:

deiban:~# apt-get install libapache2-mod-evasive

2. Enable mod-evasive in Apache

debian:~# ln -sf /etc/apache2/mods-available/mod-evasive.load /etc/apache2/mods-enabled/mod-evasive.load

3. Configure the way mod-evasive deals with potential DoS attacks

Open /etc/apache2/apache2.conf, go down to the end of the file and paste inside, below three mod-evasive configuration directives:

<IfModule mod_evasive20.c>
DOSHashTableSize 3097DOS
PageCount 30
DOSSiteCount 40
DOSPageInterval 2
DOSSiteInterval 1
DOSBlockingPeriod 120

In case of the above configuration criterias are matched, mod-evasive instructs Apache to return a 403 (Forbidden by default) error page which will conserve bandwidth and system resources in case of DoS attack attempt, especially if the DoS attack targets multiple requests to let’s say a large downloadable file or a PHP,Perl,Python script which does a lot of computation and thus consumes large portion of server CPU time.

The meaning of the above three mod-evasive config vars are as follows:

DOSHashTableSize 3097 – Increasing the DoSHashTableSize will increase performance of mod-evasive but will consume more server memory, on a busy webserver this value however should be increased
DOSPageCount 30 – Add IP in evasive temporary blacklist if a request for any IP that hits the same page 30 consequential times.
DOSSiteCount 40 – Add IP to be be blacklisted if 40 requests are made to a one and the same URL location in 1 second time
DOSBlockingPeriod 120 – Instructs the time in seconds for which an IP will get blacklisted (e.g. will get returned the 403 foribden page), this settings instructs mod-evasive to block every intruder which matches DOSPageCount 30 or DOSSiteCount 40 for 2 minutes time.
DOSPageInterval 2 – Interval of 2 seconds for which DOSPageCount can be reached.
DOSSiteInterval 1 – Interval of 1 second in which if DOSSiteCount of 40 is matched the matched IP will be blacklisted for configured period of time.

mod-evasive also supports IP whitelisting with its option DOSWhitelist , handy in cases if for example, you should allow access to a single webpage from office env consisting of hundred computers behind a NAT.
Another handy configuration option is the module capability to notify, if a DoS is originating from a number of IP addresses using the option DOSEmailNotify
Using the DOSSystemCommand in relation with iptables, could be configured to filter out any IP addresses which are found to be matching the configured mod-evasive rules.
The module also supports custom logging, if you want to keep track on IPs which are found to be trying a DoS attack against the server place in above shown configuration DOSLogDir “/var/log/apache2/evasive” and create the /var/log/apache2/evasive directory, with:
debian:~# mkdir /var/log/apache2/evasive

I decided not to log mod-evasive DoS IP matches as this will just add some extra load on the server, however in debugging some mistakenly blacklisted IPs logging is sure a must.

4. Restart Apache to load up mod-evasive debian:~# /etc/init.d/apache2 restart

Finally a very good reading which sheds more light on how exactly mod-evasive works and some extra module configuration options are located in the documentation bundled with the deb package to read it, issue:

debian:~# zless /usr/share/doc/libapache2-mod-evasive/README.gz

My E-Marketing Report Final Versus for Download ( compared to

Monday, April 4th, 2011

Some few months ago, I’ve posted some study materials for e-marketing & commerce course (discipline) that I followed in Arnhem Business School (ABS)
Apart from that I had a final assignment which was supposed to be handed in some few weeks before the begging of the Christmas break.

The Emarketing assignment’s aim was to make a comparison of two websites which are operating in the same or very similar business field

The report’s goal was to present to the E-marketing teacher which in my case was Peter Stemers that the student has been acquainted with the basic theories of Emarketing.
The project was actually rather easy and the main issue to build up a project like this is the start up to complete it you just need to put a start and persist in expanding the document.

As the topic was very interesting to myself I started quite early in preparing my assignment (just a few weeks after it was assigned).

I’ve considered my profound interest into Information and Computer Technology (ICT) and decided to create a report which evaluates two websites which are into the IT sphere.
After a examination over a few possible domain names like for example:
Verizon – and AT&T –
1& and Godaddy etc.

I’ve finally set my websites to compare choice on: and

The criterias for selection of Godaddy and Enom as a target companies to compare their online business was as follows::

1. Both Godaddy and Enom are into the same business online industry, ( e.g. domain selling, reselling, blog hosting, webhosting, SSL certificates, online presence Search Engine optimization etc.)
Some other selection factor that convinced me to choose exactly and Godaddy were that this are the biggest companies in the domain names selling IT sector and even better the Domain Selling industry has a tight relation to the History of how the Internet emerged.

The report became really thoroughful, the Godaddy vs Enom emarketing report has the size of 59 pages. Officially the study criterias has been that normally the usual student emarketing reports contains about 15 to 20 pages, however as the business products and services that this huge internet domain reseller companies has, I was forced to exceed the set teacher limitation of 20 pages and do it in 59 pages.

I’ve handed in my emarketing report and Peter Stemers graded it with 8.5 points from 10 possible (which by the way is quite a high mark for Arnhem Business School)

By the wat the E-marketing course was quite a silly one though for people that are not have an avarage computer knowledge and interest into Internet Commerce it was okay.

To read the table of contents of the Report comparison Enom compared to Godaddy click over here
Here is also my Emarketing Final Report vs ( compared to in both PDF and DOC, I hope this reports will be helpful to some marketing researchers out there to get an estimate on how the two companies are performing in the domain selling and reselling business:

1. Download My Emarketing and E-commerce report Godaddy Versus (Godaddy Compared to doc version

2. Download E-marketing report Godaddy.Com VS Enom.Com ( Compared to in PDF

Compiling this Emarketing report costed me a lot of effort and time, the overall completion of the report has took me about a two weeks time, whether each day I worked a couple of hours on it.
I express also my big thanks to Alex Petrov (a friend of mine) for helping me read and review the report and fix some minor errors in sentence structures and my language of expression.

The Godaddy VS Enom Emarketing report outlines, numerous pitfalls that both Enom Company and Go Daddy has done in terms of SEO, Emarketing, user friendliness and usability

I believe this report could be really helpful for the these two competitive companies and could help them improve both their user image, their accessibility and Search Engine indexing.
On the other hand the report could be a good example for (HAN – Arnhem Business School E-Marketing) students on how to write a good looking Emarketing report to give themselves a pass.

An interesting fact is that before I decide to publish the report online and make it available to everyone I tried a known selling marketing report, I tried to offer to both Godaddy.Com and Enom.Com to sell them this report by sending the offer to their marketing and sales guys. has returned me an email, that they will look forward to my request, whether with Godaddy I have received an email by Go Daddy founder and CEO Bob Parons and the COO Warren Adelman

I will present you here the reply just to show you how impodent this mans are! My offer to sell them this great report for the symbolic sum of 200 EUR which will help their companies grow was considered I quote: “Unsolicated Report”.
Below I present you my offer email plus the impudent reply email by GoDaddy’s CEO and CEO:

SNAP – My Email to Godaddy
Hi Bob,

My name is Georgi Georgiev and I’m currently completing my bachelor in
Business Administration in HAN University of Applied Sciences (The

Currently I’m developing an E-marketing report which is comparing the 2
largest internet domian registrars and

The report is a in depth SEO and E-marketing analysis of current
positioning in major search engines of and as well
as an overall analysis of user user friendliness, screen resolution
readiness of the two websites.
In the report I also analyse the behaviour of the and as tested with different major Internet web browsers,
general user experience. External statistical websites etc. etc.

This research document does also concludes what are the strengths &
weaknesses of both your company and The aim of the report is
to show, what Godaddy advantages and pitfalls if compared to

It also includes a number of suggestion for improvements which will be
beneficial for your company to drive more internet traffic to you as
well as increase your number of customers.

The report is 60 pages long document and includes many things that might
be beneficial for your business.

If you’re interested into the report and you’d like to buy it for me for
a very cheap price of 200 EUR, please contact me on my mail or

Best Regards,

Georgi Georgiev


SNAP – Godaddy’s Bob Parson and Warren Adelman Reply Email:

Office of the President Response
Dear Georgi Georgiev,

Thank you for contacting the Office of the President. Our CEO, Bob Parsons, and President and COO, Warren Adelman, have asked me to respond on their behalf.

We value your time and appreciate the information you have provided regarding this request. Please understand that we are not seeking to acquire any unsolicited reports of this nature at this time.

Thank you for your understanding.


Jordan McAlister

Hope this post is helpful to some students stucked with writting their E-marketing report
I also hope it shows how proficient, I’m in building reports and might be a good exapmle on how qualitative my work is and enhearten somebody to hire me as an E-marketing consultant 😉